1. Technical Field
The present invention relates to a coupling member that is used to join a wooden column to a mating member, such as a wooden beam or foundation, in a wooden building, a method for producing the coupling member, and a wooden member joint structure using the coupling member.
2. Related Art
It has been suggested to join wooden columns and wooden beams or wooden columns and the foundation by means of so-called rigid joints that allow the transmission of a bending moment therebetween to form a structural skeleton having a rigid-frame structure in a wooden building. In such a structure, when a horizontal force is applied to the structural skeleton, a bending moment acts on the joints between columns and beams or joints between columns and the foundation. When horizontal forces in opposite directions are repeatedly applied as in the case of an earthquake, bending moments in opposite directions are applied repeatedly and alternately to the joints between columns and beams or joints between columns and the foundation. The joints must have sufficient strength against such bending moments.
A joint structure for a rigid-frame structure using wooden columns is disclosed in Patent Literature 1, for example.
In this joint structure, each wooden column is joined to the foundation at two points via joint devices at a lower end thereof. Each of the joints has the following configuration.
As shown in FIG. 15, a screw member 122 is axially threaded into a lower end of a wooden column 121, and the screw member 122 has a hollow hole axially extending from an end face thereof. A joint bolt 123 is inserted into the hollow hole, and the upper end of the joint bolt 123 is threaded into the bottom of the hollow hole. The upper end of the joint bolt 123 is coupled to the screw member 122 in this way, and the lower end of the joint bolt 123 is coupled to a joint device 125 coupled to a foundation 124. Specifically, an intermediate nut 126 and a fastening nut 127 are threadedly mounted on a male thread portion 123a formed at the lower end of the joint bolt 123, and the joint device 125 is fixedly interposed between the intermediate nut 126, which has been tightened until it is in pressure contact with an end face of the screw member 122, and the fastening nut 127.
Two joints each using a screw member 122 and a joint device 125 as described above are provided at two locations at the lower end of the column 121, in other words, at both ends in the long-side (longitudinal) direction of the cross-section of the column having a flat rectangular cross-section. The joints bear a tensile force and a compressive force, respectively, to resist a bending moment.
In the above joint structure, when a large bending moment acts to a lower end of the column 121, an upward pulling force is applied to the screw member 122 in the position where one of the screw members 122 is threaded into the wooden column 121 and a tensile force acts to the joint bolt 123 threadedly inserted into the hollow hole of the screw member 122. On the other hand, a compressive force acts between the other screw member (not shown) and joint device via the intermediate nut. The joint bolt 123 to which a tensile force acts undergoes elongation in such a way that it is pulled out of the hollow hole of the screw member 122, and undergoes plastic deformation under tensile stress when the elongation exceeds its elastic limit. After that, when a bending moment in the opposite direction is generated, a force acts (the column 121 is deformed) in such a direction that the lower end of the column 121 is pressed against the joint device 125, and a compressive force acts to the joint bolt 123, which has undergone plastic deformation under tensile stress. In other words, the upper surface of the joint device 125 is pressed against the intermediate nut 126, and a compressive force acts to press the joint bolt 123 into the hollow hole of the screw member 122, whereby the intermediate nut 126 is returned to its original position where it abuts against the screw member 122.
In this way, in the above joint structure, the column 121 can be kept joined to the foundation 124 via the joint device 125 even when bending moments in opposite directions act repeatedly and alternately to the joint.
[Patent Literature 1] JP-A-2007-077611
In the joint structure disclosed in Patent Literature 1, even when bending moments in opposite directions are repeatedly applied to the joint as described above, the joint between the column 121 and the foundation 124 can be maintained and the energy of earthquake motion can be absorbed by plastic deformation of the joint bolt 123.
However, the joint structure has the following problem desired to be solved in terms of the screw member 122 and the joint bolt 123.
When horizontal forces are repeatedly applied to the joint and the joint bolt 123 undergoes plastic deformation in the tensile direction as in the case of an earthquake, the male thread portion threadedly engaged with the screw member 122 also undergoes plastic deformation in the tensile direction. There is a small play between the female thread portion formed in the bottom of the hollow hole of the screw member 122 and the male thread portion of the joint bolt 123 because of dimensional tolerances, and the screw member 122 and the joint bolt 123 can slightly wobble relative to each other. When the joint bolt 123 undergoes plastic deformation in the tensile direction, the play between them increases. When the screw member 122 and the joint bolt 123 are displaced relative to each other because of the play, the ability of the joint bolt 123 to absorb vibrational energy in the event of an earthquake decreases. Where, the ability is created as the joint bolt 123 alternately undergoes plastic deformation in the tensile direction and plastic deformation in the compressive direction.
In addition, because the angle between the axes of the female thread portion in the hollow hole of the screw member 122 and the male thread portion of the joint bolt 123 becomes likely to change, the joint bolt 123 becomes likely to undergo buckling when a compressive force is applied thereto. In other words, because the restriction on a change in the angle of the tip of the joint bolt 123 is relaxed and the buckling length of the joint bolt 123 therefore increases, the joint bolt 123 can undergo buckling under a lower load. The ability of the joint bolt 123 to absorb vibrational energy in the event of an earthquake also decreases when the joint bolt 123 undergoes buckling in the hollow hole of the screw member 122 as described above.
In addition, the screw member 122 and the joint bolt 123, the joint bolt 123 and the intermediate nut 126, and the joint bolt 123 and the fastening nut 127 are threadedly engaged with each other, these members are desired to be assembled in such a manner that no looseness will develop between them.
The present invention has been made in view of the above circumstances, and it is, therefore, an object of the present invention to provide a coupling member that enables the joint between a wooden member and a mating member to absorb vibration energy effectively, a method for producing the coupling member, and a wooden member joint structure using the coupling member.